[S9] Some apps or processes are overloading the system (CPU)

Iíve been receiving the message, ďSome apps or processes are overloading the system ( CPU) and must restartĒ, since July 4.
Battery drain has been about 39% - 50%, overnight while sleep. Is dead in the morning if I go to sleep with 39%. Is half drained after a full charge before sleep.
No problem during the day. Ive cleared app cache, wiped partition. I donít have social media or gaming apps on phone.
Started after I installed android message app, but I uninstalled on the 5th and Iím still receiving this error.
Android System is the highest % of battery usage. Sometimes it gets up to 59%. Tried toggling between its ability to allow background usage. No difference. Same issue.
Have had the phone since mid-March and has been working week; no battery/charge issues.
Help!